Inspired by this
diary I did the math. (in a comment there)
It isn't just the phone numbers they are recording.
Suppose you were to record the phone calls to and from all people in the USA.
Each record is about 24 bytes. 10 + 10 + 4 for the time.
330 million people, an average of (say) thirty a day? (remember I'm counting 2 year olds in this). Think about how many calls are on your monthly statement if you get call detail.
10 billion calls a day? By 24 bytes.
240 billion bytes a day.
I HAVE 1/20 OF THAT ON THE LAPTOP I'M TYPING THIS COMMENT ON
20 hard drives a day... is that a bleeding edge database?
They aren't recording the numbers.
They are recording the calls.
The only possible way this database could possibly be difficult is if they are recording the content of every phone call.
(If you aren't following the math, and think this is outrageous, just think of what you can store on your iPod.)
Think about the size of the Google Cache.
NSA could, with a project of just about the magnitude we are hearing about, record the content of every call. It is 56 Kbits a second, in one direction at a time, and highly compressible.
Recording just the numbers is trivial. You could do it for a few thousand dollars a day.
Reording the content of every call would be just about the database size we've been hearing about.